The use of elements coated in this manner is possible in a variety of manners and advantageous effects can be utilized. A self-cleaning effect can thus be utilized for windows or frontage elements. An independent sterilization can be utilized for the cleaning of the air with wall coverings or in vehicle passenger compartments. Organic compounds can be oxidized by reaction with oxygen to form carbon dioxide and water when the coated surface is exposed to suitable electromagnetic radiation. Photocatalytically active titanium dioxide has a high proportion of titanium dioxide for this purpose in the anatas modification. As a consequence of a bandgap at 3.2 eV, electromagnetic radiation having wavelengths below 388 nm can be utilized for exciting electron-hole pairs for initiating the reactions.
Surfaces thus coated can also be hydrophilic so that a formation of water droplets on the surface can be avoided and fogging protection can be achieved due to the formation of a water film.
In addition, microbiological growth can be prevented, but at least impeded.
Different processes are known and are also used for the formation of the titanium dioxide layers in question. In many cases, the manufacture is, however, associated with high effort and costs. Such coatings are thus formed using the most varied PVD processes. In this respect, the effort is, however, substantial due to the required vacuum technology.
Sol-gel processes and thermal oxidation processes require very high temperatures and can therefore not be used for the coating of all materials. The time effort for this is likewise high. The layers can also be sprayed on thermally, which, however, causes a low layer quality and rough surfaces.
CVD processes under vacuum conditions with and without plasma assistance or photon assistance have similar disadvantages to PVD processes.
An approach using a CVD process under normal atmospheric pressure is known from EP 1 650 325 A1. In this respect, in particular a formation of powder should be avoided which can normally not be avoided in such processes and impairs the plant engineering and the layer quality. It is proposed therein to form a metal oxide layer on a surface with the aid of gas phase hydrolysis. For titanium dioxide layers in this respect, in particular gaseous TiCl4 and water vapor should be used as gases which chemically react with one another on contact. To avoid the formation of powder, it is proposed therein to utilize a shortened contact time of the two gases reacting with one another which should be 1 s at a maximum. A layer with titanium can thereby be obtained on the surface which can subsequently be calcinated at temperatures above 300° C. and only thereby can the ultimately photocatalytically active titanium dioxide layer be obtained.
It is obvious that the additional process step—calcination—increases the manufacturing effort and also that not all materials can be coated in this manner due to the temperatures required for it.